As the other answer says, it might be the mirror isn't completely up to date, or perhaps the updates were pushed out partially. You can try yum clean metadata (that blows away yum's idea of available packages, etc, but not what it has already downloaded), and try again, adding --skip-broken (that omits packages that can't be updated for whatever reason). Maybe you need a few rounds of doing this. Look at the package it is complaining about, try yum reinstall that. Consider running package-cleanup (from the yum-utils package), it helps in fixing a lot of inconsistencies.